TPM’s Josh Marshall has shared a chart of their mobile (smartphone + tablet, in this case) traffic growth, which is substantial. Highlights:

— Mobile now accounts for 19 percent of TPM traffic.

— It’s iPhone, iPad, and Android, in that order. No other platform matters much. TPM gets around 750,000 visits a month from iPhones, 500,000 from iPads, and 400,000 from Android devices.

— iPhone growth is accelerating.

— Marshall: “My own sense is that iPhone or other handset devices will never be the primary way people will want to read news. It’s just too small — totally functional and extremely useful but not what you’d probably gravitate towards if you were at home and had a desktop or tablet to use. But I can easily imagine tablets becoming the preferred way to reading news.”

As a regular TPM reader, I suspect they’d see even faster mobile growth if they integrated the TPMLiveWire — which seems tailor-made for mobile, being a series of quick bursts of news — into their mobile site. It’s a curious absence.